Diffraction of a wave passing through double slits
Quality is butchered by gif format



You will need 3 Dynamic Paint objects



Canvas

Highly subdivided Plane with this settings:



Most important thing here is to set Timescale to 0.10 and Speed to 5. I don't know why but this way whole simulation is more stable.

Collision object

This is just a Brush with Waves > Type > Reflect Only



Wave generator

Animated Cylinder Brush with Waves > Type > Depth Change. Also you can crank up Factor and Clamp Waves. Seems like these options are producing smoother result.



Blend file

Here is file with used material and everything else: